The dilemma I am 23 and have been with my partner since we were 17. He is my first serious relationship and the only person I have been intimate with. During secondary school he dated a girl who unfortunately died. I'm so jealous of their situation because they have a link I can't compete with. I know it wasn't love, but it's the significance that he had a girlfriend who died while he was with her. I wish he could mourn me, too. I want to connect with him in every way his past relationships have. I think I'm jealous of all his female relationships, even his mother. I'm even jealous of his female dog. I don't want to be like this, but don't know how to change. The things I have expressed may seem crazy, but I would hate for this to be the end of the relationship because I love him dearly.

Mariella replies Not crazy, but ever so young! Letters like yours make me relieved to be middle-aged. There is nothing more annoying than having your trials and tribulations linked directly to your immaturity, but here I have little choice. Some conditions are almost entirely the result of inexperience, and the kind of deep-rooted insecurity that is – thankfully – generally only found in the very young. Your jealousy ticks all those boxes, and while you might argue that at 23 you are well into your adulthood, when it comes to the vagaries of love you're on the starting block. As you mature you'll realise that a monopoly on a lover's affections is neither possible nor desirable. Relationships can be similarly intense, but without that obsessive quality; and it's the nuances that make life interesting, whether you're talking about partners or friends. When I was pregnant with my second child I spent the entire nine months in fear of being unable to love the newcomer because I was so enthralled by my 13-month-old daughter. Yet the minute her baby brother arrived, my hitherto brimful heart revealed itself to have endless space for him, too. As human beings we have an infinite capacity to love (and hate), the former being one of our most impressive virtues.

The more you try to limit an individual's experiences, erect walls to pen them in or curtail their liberty, the more they'll put into their battle to escape. You're right to fear for your relationship, because your inability to share your boyfriend with the world outside will ultimately make a prison out of what was a love affair. No relationship has ever ended because partners allowed each other room to breathe, but plenty have suffocated thanks to a lack of oxygen. There are many "classic" novels written by young authors reflecting sentiments similar to yours (the Russians being a case in point), but you'd be hard pushed to find a romantic novel by anyone over 30 that reflected a similar variety of angst. That's because the terrible sense your passion is under threat from every corner fades as fast as your experiences accumulate.

Your condition is curable, but the medicine may be hard to swallow. Along with all the delights of youth come two qualifying elements: insecurity and a myopic tendency. Here both have combined to seriously challenge your common sense and put under threat what seems a perfectly good relationship. Like you, I too was once handicapped by jealousy, unable to control my anxieties enough to enjoy my relationships. One love affair during my late teens with an older boy who, unlike me, had travelled in Europe remains a perfect example. My love for him was only rivalled by my debilitating obsession with a past love of his, a French girl he'd had a holiday romance with. I could barely kiss him without imagining him kissing her in the dappled sunlight of Provence, and I imagined her as some Bardoesque nymphette. I knew I'd never compete with her exotic allure, a conviction compounded by the belief in 70s Ireland that all French girls were man eaters with voracious sexual appetites. My fears were realised when I found a photo of her under his bed. Her image surpassed even my most fecund nightmares: tumbling hair, full lips, a come-hither stare. No wonder he kept her in handy reach. I nursed this secret discovery for days, terrified to admit that I'd been snooping around his bedroom but eaten up with this evidence of his mental infidelity. Finally I challenged him, only to discover it was a picture of his favourite singer, Carly Simon, that had fallen out of his guitar manual. My embarrassment was intense, but sadly not strong enough to prevent me from continuing to police his every move and obsess about his past until he finally had to be rid of me.

It's a salutary lesson: that your worst fears are often based on what you yourself are capable of destroying, not what others may do to you. So, my young friend, if you don't want to lose this boy, then for heaven's sake stop following in my flawed footsteps. In our lives the greatest danger rarely lurks in the past but in our future.